%template scope enforcement and class definition fixes

The scoping rules around %template have been specified and enforced.
The %template directive for a class template is the equivalent to an
explicit instantiation of a C++ class template. The scope for a valid
%template instantiation is now the same as the scope required for a
valid explicit instantiation of a C++ template. A definition of the
template for the explicit instantiation must be in scope where the
instantiation is declared and must not be enclosed within a different
namespace.

For example, a few %template and explicit instantiations of std::vector
are shown below:

  // valid
  namespace std {
    %template(vin) vector<int>;
    template class vector<int>;
  }

  // valid
  using namespace std;
  %template(vin) vector<int>;
  template class vector<int>;

  // valid
  using std::vector;
  %template(vin) vector<int>;
  template class vector<int>;

  // ill-formed
  namespace unrelated {
    using std::vector;
    %template(vin) vector<int>;
    template class vector<int>;
  }

  // ill-formed
  namespace unrelated {
    using namespace std;
    %template(vin) vector<int>;
    template class vector<int>;
  }

  // ill-formed
  namespace unrelated {
    namespace std {
      %template(vin) vector<int>;
      template class vector<int>;
    }
  }

  // ill-formed
  namespace unrelated {
    %template(vin) std::vector<int>;
    template class std::vector<int>;
  }

When the scope is incorrect, an error now occurs such as:

cpp_template_scope.i:34: Error: 'vector' resolves to 'std::vector' and
was incorrectly instantiated in scope 'unrelated' instead of within scope 'std'.

Previously SWIG accepted the ill-formed examples above but this led to
numerous subtle template scope problems especially in the presence of
using declarations and using directives as well as with %feature and %typemap.

Actually, a valid instantiation is one which conforms to the C++03
standard as C++11 made a change to disallow using declarations and
using directives to find a template.

  // valid C++03, ill-formed C++11
  using std::vector;
  template class vector<int>;

Similar fixes for defining classes using forward class references have
also been put in place. For example:

namespace Space1 {
  struct A;
}
namespace Space2 {
  struct Space1::A {
    void x();
  }
}

will now error out with:

cpp_class_definition.i:5: Error: 'Space1::A' resolves to 'Space1::A' and
was incorrectly instantiated in scope 'Space2' instead of within scope 'Space1'.

Examples/test-suite/errors/cpp_class_definition.i

@@ -0,0 +1,26 @@
+%module xxx
+
+// This should error but doesn't
+#if 0
+namespace OtherSpace {
+  struct L;
+}
+namespace Space11 {
+  namespace SubSpace11 {
+    using OtherSpace::L;
+    struct L {
+      void ll();
+    };
+  }
+}
+#endif
+
+namespace Space1 {
+  struct A;
+}
+namespace Space2 {
+  struct Space1::A {
+    void x();
+  };
+}
+